Process for preparing a conductive composition using a masterbatch

ABSTRACT

A composition can include polystyrene, modified-polystyrene, or a mixture thereof. The polystyrene, modified-polystyrene, or mixture thereof can include carbon nanotubes. The composition can also include a polyolefin. The composition can include at most 1.90% by weight of carbon nanotubes, based on a total weight of the composition. The composition can be prepared by providing a masterbatch including at least 5% by weight of carbon nanotubes based on a total weight of the masterbatch, and a polyolefin and/or styrenic copolymer. The masterbatch can be blended with polystyrene, modified-polystyrene, or a mixture thereof, and with a polyolefin, in amounts such that a conductive composition is obtained. An article can be made of the conductive composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT/EP2013/050964, filed on Jan.18, 2013, which claims priority from European Application No.12151931.8, filed on Jan. 20, 2012, and PCT/EP2012/072471, filed on Nov.13, 2012.

FIELD OF THE INVENTION

The present invention relates to a polymer composition comprising carbonnanotubes. In particular, the present invention relates to conductivepolymer compositions comprising carbon nanotubes. The present inventionalso relates to a process for the preparation of said compositions.

BACKGROUND OF THE INVENTION

As electronic devices become smaller and faster, their sensitivity toelectrostatic charges is increased and electronic packaging has beenprovided to improve electrostatically dissipative properties.Electronics packaging is designed to prevent the build-up of staticelectrical charges and the consecutive electrostatic discharge (ESD)which can be responsible of serious damages to sensitive electronics andresult in product defects and high scrap rates.

In order to ensure ESD protection, inherently electrically insulatingpolymers may be rendered conductive or dissipative by incorporatingconductive fillers (such as carbon black, CB) allowing effectivedissipation of static electrical charges.

Currently conductive or dissipative plastics are dominated by CB, mainlybecause CB is relatively cheap in comparison to other conductivefillers, such as carbon fiber, carbon nanotubes (CNT), metal fiber,metal-coated carbon fiber, and metal powder. Addition level of CB mustbe sufficient so that particles create a conductive pathway through thematerials. In consequence, high levels of CB (15-30%) are required tomeet the requirements, which alter critical physical properties of thebasic polymer such as impact strength, elongation and compoundviscosity.

These properties need to be preserved when using other fillers insteadof CB as conductive fillers. Nevertheless, a minimum concentration isrequired to obtain the desired conductivity. Since other fillers aremore expensive than CB, there remains a need to provide improvedconductive compositions which are electrically insulating.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aconductive composition which is electrically insulating. According to afirst aspect, the invention provides a process for preparing aconductive composition, said process comprising the steps of (a)providing a masterbatch comprising at least 5% by weight of carbonnanotubes based on the total weight of the masterbatch, and a polyolefinand/or styrenic copolymer; (b) blending the masterbatch of step (a) withpolystyrene or modified-polystyrene or mixture thereof, and with apolyolefin, in amounts such that conductive composition is obtainedwhich comprises at most 1.90% by weight of carbon nanotubes based on thetotal weight of the composition.

The independent and dependent claims set out particular and preferredfeatures of the invention. Features from the dependent claims may becombined with features of the independent or other dependent claims asappropriate.

DETAILED DESCRIPTION OF THE INVENTION

Before the present compositions and processes of the invention aredescribed, it is to be understood that this invention is not limited toparticular compositions described, since such compositions may, ofcourse, vary. It is also to be understood that the terminology usedherein is not intended to be limiting, since the scope of the presentinvention will be limited only by the appended claims.

In the following passages, different aspects of the invention aredefined in more detail. Each aspect so defined may be combined with anyother aspect or aspects unless clearly indicated to the contrary. Inparticular, any feature indicated as being preferred or advantageous maybe combined with any other feature or features indicated as beingpreferred or advantageous.

As used herein, the singular forms “a”, “an”, and “the” include bothsingular and plural referents unless the context clearly dictatesotherwise. By way of example, “a polystyrene” means one polystyrene ormore than one polystyrene.

The terms “comprising”, “comprises” and “comprised of” as used hereinare synonymous with “including”, “includes” or “containing”, “contains”,and are inclusive or open-ended and do not exclude additional,non-recited members, elements or method steps. It will be appreciatedthat the terms “comprising”, “comprises” and “comprised of” as usedherein comprise the terms “consisting of”, “consists” and “consists of”.

The recitation of numerical ranges by endpoints includes all integernumbers and, where appropriate, fractions subsumed within that range(e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, anumber of elements, and can also include 1.5, 2, 2.75 and 3.80, whenreferring to, for example, measurements). The recitation of end pointsalso includes the end point values themselves (e.g. from 1.0 to 5.0includes both 1.0 and 5.0). Any numerical range recited herein isintended to include all sub-ranges subsumed therein.

All references cited in the present specification are herebyincorporated by reference in their entirety. In particular, theteachings of all references herein specifically referred to areincorporated by reference.

The present invention provides a conductive composition comprising apolystyrene or modified-polystyrene or mixture thereof, wherein thecomposition further comprises a polyolefin; and wherein the compositionfurther comprises at most 1.90% by weight of carbon nanotubes, based onthe total weight of the composition.

In an embodiment, the composition comprises the melt blending product ofsaid polystyrene or modified-polystyrene or mixture thereof, saidpolyolefin and said carbon nanotubes.

As used herein, the term “melt blending” involves the use of shearforce, extensional force, compressive force, ultrasonic energy,electromagnetic energy, thermal energy or combinations comprising atleast one of the foregoing forces or forms of energy and is conducted inprocessing equipment wherein the aforementioned forces are exerted by asingle screw, multiple screws, intermeshing co-rotating or counterrotating screws, non-intermeshing co-rotating or counter rotatingscrews, reciprocating screws, screws with pins, barrels with pins,rolls, rams, helical rotors, or combinations comprising at least one ofthe foregoing. Melt blending may be conducted in machines such as,single or multiple screw extruders, Buss kneader, Eirich mixers,Henschel, helicones, Ross mixer, Banbury, roll mills, molding machinessuch as injection molding machines, vacuum forming machines, blowmolding machines, or the like, or combinations comprising at least oneof the foregoing machines. It is generally desirable during melt orsolution blending of the composition to impart a specific energy ofabout 0.01 to about 10 kilowatt-hour/kilogram (kwhr/kg) of thecomposition. In a preferred embodiment, melt blending is performed in atwin screw extruder, such as a Brabender co-rotating twin screwextruder.

Preferably, the composition comprises at least two immiscible phases: apolystyrene phase and a polyolefin phase.

In some embodiments, the composition can comprise at least 30% by weightof the polystyrene or modified-polystyrene or mixture thereof, based onthe total weight of the composition. Preferably, the compositioncomprises at least 35% by weight, for example at least 40% by weight,for example at least 45% by weight, more preferably at least 50% byweight of the polystyrene or modified-polystyrene or mixture thereof,yet more preferably at least 54% by weight of the polystyrene ormodified-polystyrene or mixture thereof, based on the total weight ofthe composition.

Non-limiting examples of suitable polystyrenes which can be used in thecomposition comprise polystyrene, modified polystyrene, or mixtures ofpolystyrene and modified polystyrene.

In the modified-polystyrene, part of the styrene may be replaced byunsaturated monomers copolymerizable with styrene, for examplealpha-methylstyrene or (meth)acrylates, Other examples which may bementioned are chloropolystyrene, poly-alpha-methylstyrene,styrene-chlorostyrene copolymers, styrene-propylene copolymers,styrenebutadiene copolymers, styrene-isoprene copolymers, styrene-vinylchloride copolymers, styrene-vinyl acetate copolymers, styrene-alkylacrylate copolymers (methyl, ethyl, butyl, octyl, phenyl acrylate),styrene-alkyl methacrylate copolymers (methyl, ethyl, butyl, phenylmethacrylate), styrene methyl chloroacrylate copolymers andstyrene-acrylonitrile-alkyl acrylate copolymers.

The polystyrenes for use in the present invention may be co- orhomopolymers of styrene, alpha methyl styrene and para methyl styrene.Preferably the polystyrene is homopolystyrene.

The polystyrenes may be prepared by a number of methods. This process iswell known to those skilled in the art and described for example in theabove mentioned reference.

The modified-polystyrene for use in the composition may be rubbermodified.

The rubber may be prepared by a number of methods, preferably byemulsion or solution polymerization. These processes are well known tothose skilled in the art.

If present, preferably the rubber is present in an amount from about 3to 15% by weight. Polybutadiene is a particularly useful rubber.

Preferably the modified-polystyrene is rubber modified polystyrene.

In an embodiment, the rubber modified polystyrene is a High ImpactPolystyrene (HIPS). The process for making HIPS is well known to thoseskilled in the art. For example, the process may comprise polymerizingstyrene monomer in the presence of dissolved rubber. Polymerization ofstyrene, and optionally a comonomer, may be initiated by heating and/orby an initiator, by way of example a radical initiator. The rubber maybe “dissolved” in the styrene monomer. The usual rubber types utilizedin the manufacture of HIPS include polybutadiene (PB), styrene-butadienerubber (SBR), and styrene-butadiene-styrene rubber (SBS). Polystyrenemay be initially formed from the styrene monomer within the homogeneousrubber solution in styrene. In HIPS, a part of the styrene may bereplaced by unsaturated monomers copolymerizable with styrene such asother monovinylaromatic monomers, alkyl esters of acrylic or methacrylicacid and acrylonitrile. Non-limiting examples of suitable processes forpreparing HIPS are described in US2010/240832, incorporated herein byreference.

Advantageously, the modified-polystyrene is a HIPS or a mixture ofpolystyrene and HIPS.

In an embodiment, the composition comprises at least 30% by weight HIPSor a mixture of polystyrene and HIPS, based on the total weight of thecomposition. For example, the composition comprises at least 35%, atleast 40%, at least 45%, at least 50% by weight of HIPS or a mixture ofHIPS and polystyrene, based on the total weight of the composition.

The composition also comprises at least one polyolefin. As used herein,the terms “olefin polymer” and “polyolefin” are used interchangeably.

In an embodiment, the composition comprises at most 70%, for example atmost 60%, by weight of polyolefin based on the total weight of thecomposition. For example, the composition comprises at least 15% byweight, for example at least 20%, for example at least 25%, for exampleat least 30% of polyolefin based on the total weight of the composition,preferably at least 35% of polyolefin based on the total weight of thecomposition, preferably at least 40% of polyolefin based on the totalweight of the composition.

Suitable polyolefins used in the present invention may be any olefinhomopolymer or any copolymer of an olefin and one or more comonomers. Asused herein, the term “homo-polymer” refers to a polymer which is madeby linking (preferably olefin, preferably ethylene) monomers, in theabsence of comonomers. As used herein, the term “co-polymer” refers to apolymer, which is made by linking two different types of monomers in thesame polymer chain. The polyolefins may be atactic, syndiotactic orisotactic. The olefin can be mono-olefin, of di-olefin. The mono-olefincan for example be ethylene, propylene, 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene or 1-octene, but also cycloolefins such as forexample cyclopentene, cyclohexene, cyclooctene or norbornene. Preferablythe olefin is alpha-olefin. The di-olefin can for example also bebutadiene (such as 1,3-butadiene), 1,2-propadiene,2-methyl-1,3-butadiene, 1,5-cyclooctadiene, norbornadiene,dicyclopentadiene, 1,3-heptadiene, 2,3-dimethylbutadiene,2-ethyl-1,3-pentadiene, 1,3-hexadiene or 2,4-hexadiene.

The comonomer if present is different from the olefin and chosen suchthat it is suited for copolymerization with the olefin. The comonomermay also be an olefin as defined above. Comonomers may comprise but arenot limited to aliphatic C₂-C₂₀ alpha-olefins. Examples of suitablealiphatic C₂-C₂₀ alpha-olefins include ethylene, propylene, 1-butene,4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene,1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. Furtherexamples of suitable comonomers are vinyl acetate (H₃C—C(═O)O—CH═CH₂) orvinyl alcohol (“HO—CH═CH₂”, which as such is not stable and tends topolymerize). Examples of olefin copolymers suited for use in the presentcomposition are random copolymers of propylene and ethylene, randomcopolymers of propylene and 1-butene, heterophasic copolymers ofpropylene and ethylene, ethylene-butene copolymers, ethylene-hexenecopolymers, ethylene-octene copolymers, copolymers of ethylene and vinylacetate (EVA), copolymers of ethylene and vinyl alcohol (EVOH).

The amount of comonomer can be from 0 to 12% by weight, based on theweight of the polyolefin, more preferably it can be from 0 to 9% byweight and most preferably it can be from 0 to 7% by weight. A copolymercan be a random or block (heterophasic) copolymer. Preferably, thecopolymer is a random copolymer.

Preferred polyolefins for use in the present composition are olefinhomopolymers and copolymers of an olefin and optionally one or morecomonomers. In a preferred embodiment, the polyolefin is a homopolymeror a copolymer of ethylene, or propylene. In an embodiment, thepolyolefin is selected from the group comprising polyethylene,polypropylene or a combination thereof. Preferably, the polyolefin isselected from polyethylene and polypropylene homo- and copolymers.Preferably, the polyolefin is polyethylene or polypropylene, or acopolymer thereof.

In a preferred embodiment, the polyolefin is selected from the groupcomprising linear low density polyolefin, low density polyolefin, andhigh density polyolefin.

In an embodiment, the polyolefin has a density of 0.890 to 0.975 g/cm³,preferably of from 0.890 to 0.960 g/cm³, preferably of from 0.890 to0.930 g/cm³, preferably of from 0.890 to 0.925 g/cm³, preferably of from0.890 to 0.920 g/cm³ with the density being determined with the ASTMD-1505 standardized test at a temperature of 23° C.

Preferably the polyolefin is a linear low density polyolefin.Preferably, the polyolefin is selected from the group comprising linearlow density polyethylene (LLDPE), low density polyethylene (LDPE), andhigh density polyethylene (HDPE). Suitable Linear low densitypolyethylene (LLDPE) and low density polyethylene (LDPE) has a densitybelow 0.930 g/cm³ with the density being determined with the ASTM D-1505standardized test at a temperature of 23° C. Suitable high densitypolyethylene (HDPE) has a density ranging from 0.940 to 0.975 g/cm³,with the density being determined with the ASTM D-1505 standardized testat a temperature of 23° C. Preferably the polyolefin is linear lowdensity polyethylene (LLDPE).

Suitable linear low density polyethylenes are available commercially,e.g. from Total Petrochemicals, from Exxon under the tradename Escoreneor from Dow Chemicals under the tradename DOWLEX. Alternatively, theymay readily be prepared by state of the art polymerization processessuch as those described in U.S. Pat. No. 4,354,009, U.S. Pat. No.4,076,698, European Patent Application 4645 (published Oct. 17, 1979),and U.S. Pat. No. 4,128,607. Suitable linear low density polyethylenepolymers can be co-polymers of ethylene and a minor amount, for exampleless than 20 mole %, preferably less than 15 mole %, of an alpha olefinof 3 to 18 carbon atoms, preferably 3 to 10 carbon atoms, mostpreferably 4 to 8 carbon atoms.

Preferred linear low density polyethylene co-polymers can be preparedfrom ethylene and one or more alpha olefins selected from the groupconsisting of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,1-hexene and 1-octene, most preferably 1-butene. Polymers of desireddensity may be obtained by controlling the co-polymerization ratio ofalpha olefin and the formation proportion of the polymer duringco-polymerization. The addition of increasing amounts of the co-monomersto the co-polymers results in lowering the density of the co-polymer.

The polyolefin, such as polyethylene, can be prepared as know in theart, in the presence of any catalyst known in the art. As used herein,the term “catalyst” refers to a substance that causes a change in therate of a polymerization reaction without itself being consumed in thereaction. In the present invention, it is especially applicable tocatalysts suitable for the polymerization of ethylene to polyethylene.These catalysts will be referred to as ethylene polymerization catalystsor polymerization catalysts. In an embodiment of the invention, thepolymer composition comprises a polyolefin prepared in the presence of acatalyst selected from a Ziegler-Natta catalyst, a metallocene catalystor a chromium catalyst. In a preferred embodiment of the invention, thepolymer composition comprises a polyolefin prepared in the presence of acatalyst selected from a Ziegler-Natta catalyst, a metallocene catalyst,or both; preferably prepared in the presence of a metallocene catalyst.

The term “chromium catalysts” refers to catalysts obtained by depositionof chromium oxide on a support, e.g. a silica or aluminum support.Illustrative examples of chromium catalysts comprise but are not limitedto CrSiO₂ or CrAl₂O₃.

The term “Ziegler-Natta catalyst” or “ZN catalyst” refers to catalystshaving a general formula M¹X_(v), wherein M¹ is a transition metalcompound selected from group IV to VII from the periodic table ofelements, wherein X is a halogen, and wherein v is the valence of themetal. Preferably, M¹ is a group IV, group V or group VI metal, morepreferably titanium, chromium or vanadium and most preferably titanium.Preferably, X is chlorine or bromine, and most preferably, chlorine.Illustrative examples of the transition metal compounds comprise but arenot limited to TiCl₃ and TiCl₄. Suitable ZN catalysts for use in theinvention are described in U.S. Pat. No. 6,930,071 and U.S. Pat. No.6,864,207, which are incorporated herein by reference.

The term “metallocene catalyst” is used herein to describe anytransition metal complexes consisting of metal atoms bonded to one ormore ligands. The metallocene catalysts are compounds of Group 4transition metals of the Periodic Table such as titanium, zirconium,hafnium, etc., and have a coordinated structure with a metal compoundand ligands composed of one or two groups of cyclo-pentadienyl, indenyl,fluorenyl or their derivatives. The structure and geometry of themetallocene can be varied to adapt to the specific need of the producerdepending on the desired polymer. Metallocenes comprise a single metalsite, which allows for more control of branching and molecular weightdistribution of the polymer. Monomers are inserted between the metal andthe growing chain of polymer.

In an embodiment, the metallocene catalyst has a general formula (I) or(II):(Ar)₂MQ₂  (I); orR¹(Ar)₂MQ₂  (II)

wherein the metallocenes according to formula (I) are non-bridgedmetallocenes and the metallocenes according to formula (II) are bridgedmetallocenes;

wherein said metallocene according to formula (I) or (II) has two Arbound to M which can be the same or different from each other;

wherein Ar is an aromatic ring, group or moiety and wherein each Ar isindependently selected from the group consisting of cyclopentadienyl,indenyl, tetrahydroindenyl or fluorenyl, wherein each of said groups maybe optionally substituted with one or more substituents eachindependently selected from the group consisting of halogen, ahydrosilyl, a SiR² ₃ group wherein R² is a hydrocarbyl having 1 to 20carbon atoms, and a hydrocarbyl having 1 to 20 carbon atoms, whereinsaid hydrocarbyl optionally contains one or more atoms selected from thegroup comprising B, Si, S, O, F, Cl and P;

wherein M is a transition metal selected from the group consisting oftitanium, zirconium, hafnium and vanadium; and preferably is zirconium;

wherein each Q is independently selected from the group consisting ofhalogen; a hydrocarboxy having 1 to 20 carbon atoms; and a hydrocarbylhaving 1 to 20 carbon atoms and wherein said hydrocarbyl optionallycontains one or more atoms selected from the group comprising B, Si, S,O, F, Cl and P; and

wherein R¹ is a divalent group or moiety bridging the two Ar groups andselected from the group consisting of a C₁-C₂₀ alkylene, a germanium, asilicon, a siloxane, an alkylphosphine and an amine, and wherein said R¹is optionally substituted with one or more substituents eachindependently selected from the group consisting of halogen, ahydrosilyl, a SiR³ ₃ group wherein R³ is a hydrocarbyl having 1 to 20carbon atoms, and a hydrocarbyl having 1 to 20 carbon atoms, whereinsaid hydrocarbyl optionally contains one or more atoms selected from thegroup comprising B, Si, S, O, F, Cl and P.

The term “hydrocarbyl having 1 to 20 carbon atoms” as used herein isintended to refer to a moiety selected from the group comprising alinear or branched C₁-C₂₀ alkyl; C₃-C₂₀ cycloalkyl; C₆-C₂₀ aryl; C₇-C₂₀alkylaryl and C₇-C₂₀ arylalkyl, or any combinations thereof. Exemplaryhydrocarbyl groups are methyl, ethyl, propyl, butyl, amyl, isoamyl,hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl, 2-ethylhexyl, andphenyl. Exemplary halogen atoms include chlorine, bromine, fluorine andiodine and of these halogen atoms, fluorine and chlorine are preferred.

As used herein, the term “alkyl” by itself or as part of anothersubstituent, refers to a straight or branched saturated hydrocarbonradical group joined by single carbon-carbon bonds having 1 or morecarbon atoms, for example 1 to 20 carbon atoms, for example 1 to 12carbon atoms, for example 1 to 6 carbon atoms, for example 1 to 4 carbonatoms, for example 2 to 3 carbon atoms. When a subscript is used hereinfollowing a carbon atom, the subscript refers to the number of carbonatoms that the named group may contain. Thus, for example, C₁₋₁₂alkylmeans an alkyl of 1 to 12 carbon atoms. Examples of C₁₋₁₂alkyl groupsare methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,tert-butyl, pentyl and its chain isomers, hexyl and its chain isomers,heptyl and its chain isomers, octyl and its chain isomers, nonyl and itschain isomers, decyl and its chain isomers, undecyl and its chainisomers, dodecyl and its chain isomers.

As used herein, the term “C₃₋₂₀cycloalkyl”, by itself or as part ofanother substituent, refers to a saturated or partially saturated cyclicalkyl radical containing from 3 to 20 carbon atoms. Examples ofC₃₋₂₀cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl and cyclooctyl.

As used herein, the term “C₆₋₂₀aryl”, by itself or as part of anothersubstituent, refers to a polyunsaturated, aromatic hydrocarbyl grouphaving a single ring (i.e. phenyl) or multiple aromatic rings fusedtogether (e.g. naphthalene), or linked covalently, typically containing6 to 20 carbon atoms; wherein at least one ring is aromatic. Examples ofC₆₋₂₀aryl include phenyl, naphthyl, indanyl, biphenyl, or1,2,3,4-tetrahydro-naphthyl.

The term “arylalkyl”, as a group or part of a group, refers to an alkylas defined herein, wherein one or more hydrogen atoms are replaced by anaryl as defined herein. Examples of arylalkyl radicals include benzyl,phenethyl, dibenzylmethyl, methylphenylmethyl, 3-(2-naphthyl)-butyl, andthe like.

As used herein, the term “alkylaryl”, by itself or as part of anothersubstituent, refers to an aryl group as defined herein, wherein one ormore hydrogen atoms are replaced by an alkyl as defined herein.

The term “hydrocarboxy having 1 to 20 carbon atoms” refers to a radicalhaving the formula —O—R_(a) wherein R_(a) is hydrocarbyl having 1 to 20carbon atoms. Preferred hydrocarboxy groups are alkoxy groups. The term“alkoxy” or “alkyloxy” as used herein refers to a radical having theformula —O—R_(b) wherein R_(b) is alkyl. Non-limiting examples ofsuitable alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy,butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, amyloxy,hexyloxy, heptyloxy and octyloxy. Preferred hydrocarboxy groups aremethoxy, ethoxy, propoxy, butoxy, and amyloxy.

Illustrative examples of metallocene catalysts comprise but are notlimited to bis(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂),bis(cyclopentadienyl) titanium dichloride (Cp₂TiCl₂),bis(cyclopentadienyl) hafnium dichloride (Cp₂HfCl₂);bis(tetrahydroindenyl) zirconium dichloride, bis(indenyl) zirconiumdichloride, and bis(n-butyl-cyclopentadienyl) zirconium dichloride,ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride,ethylenebis(1-indenyl) zirconium dichloride, dimethylsilylenebis(2-methyl-4-phenyl-inden-1-yl) zirconium dichloride,diphenylmethylene (cyclopentadienyl)(fluoren-9-yl) zirconium dichloride,and dimethylmethylene[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl) zirconiumdichloride.

The metallocene catalysts can be provided on a solid support. Thesupport can be an inert solid, organic or inorganic, which is chemicallyunreactive with any of the components of the conventional metallocenecatalyst. Suitable support materials for the supported catalyst of thepresent invention include solid inorganic oxides, such as silica,alumina, magnesium oxide, titanium oxide, thorium oxide, as well asmixed oxides of silica and one or more Group 2 or 13 metal oxides, suchas silica-magnesia and silica-alumina mixed oxides. Silica, alumina, andmixed oxides of silica and one or more Group 2 or 13 metal oxides arepreferred support materials. Preferred examples of such mixed oxides arethe silica-aluminas. Most preferred is silica. The silica may be ingranular, agglomerated, fumed or other form. The support is preferably asilica compound. In a preferred embodiment, the metallocene catalyst isprovided on a solid support, preferably a silica support.

Preferably, the metallocene catalyst is activated with a cocatalyst. Thecocatalyst, which activates the metallocene catalyst component, can beany cocatalyst known for this purpose such as an aluminum-containingcocatalyst, a boron-containing cocatalyst or a fluorinated catalyst. Thealuminum-containing cocatalyst may comprise an alumoxane, an alkylaluminum, a Lewis acid and/or a fluorinated catalytic support.

In an embodiment, alumoxane is used as an activating agent for themetallocene catalyst. The alumoxane can be used in conjunction with acatalyst in order to improve the activity of the catalyst during thepolymerization reaction.

As used herein, the term “alumoxane” and “aluminoxane” are usedinterchangeably, and refer to a substance, which is capable ofactivating the metallocene catalyst. In an embodiment, alumoxanescomprise oligomeric linear and/or cyclic alkyl alumoxanes. In a furtherembodiment, the alumoxane has formula (III) or (IV)

R^(a)—(Al(R^(a))—O)_(x)—AlR^(a) ₂ (III) for oligomeric, linearalumoxanes; or

(—Al(R^(a))—O—)_(y) (IV) for oligomeric, cyclic alumoxanes

wherein x is 1-40, and preferably 10-20;

wherein y is 3-40, and preferably 3-20; and

wherein each R^(a) is independently selected from a C₁-C₈alkyl, andpreferably is methyl.

In a preferred embodiment, the alumoxane is methylalumoxane (MAO).

In an embodiment, the catalyst used for preparing the polyolefin is asupported metallocene-alumoxane catalyst comprising a metallocene and analumoxane which are bound on a porous silica support.

In an embodiment, the composition can comprise at most 1.90% by weightof carbon nanotubes (CNT), based on the total weight of the composition.

Suitable carbon nanotubes used in the present invention can generally becharacterized by having a size from 1 nm to 500 nm, this definition ofsize can be limited to two dimensions only, i.e. the third dimension maybe outside of these limits.

Suitable carbon nanotubes also referred to as “nanotubes” herein, can becylindrical in shape and structurally related to fullerenes, an exampleof which is Buckminster fullerene (C₆₀). Suitable carbon nanotubes maybe open or capped at their ends. The end cap may for example be aBuckminster-type fullerene hemisphere. Suitable carbon nanotubes used inthe present invention can comprise more than 90%, more preferably morethan 95%, even more preferably more than 99% and most preferably morethan 99.9% of their total weight in carbon. However, minor amounts ofother atoms may also be present.

Suitable carbon nanotubes to be used in the present invention can beprepared by any method known in the art. They can be prepared by thecatalyst decomposition of hydrocarbons, a technique that is calledCatalytic Carbon Vapor Deposition (CCVD). Other methods for preparingcarbon nanotubes include the arc-discharge method, the plasmadecomposition of hydrocarbons or the pyrolysis of selected polyolefinunder selected oxidative conditions. The starting hydrocarbons can beacetylene, ethylene, butane, propane, ethane, methane or any othergaseous or volatile carbon-containing compound. The catalyst, ifpresent, is used in either pure or in supported form. The presence of asupport greatly improves the selectivity of the catalysts but itcontaminates the carbon nanotubes with support particles, in addition tothe soot and amorphous carbon prepared during pyrolysis. Purificationcan remove these by-products and impurities. This can be carried outaccording to the following two steps:

-   1) the dissolution of the support particles, typically carried out    with an appropriate agent that depends upon the nature of the    support and-   2) the removal of the pyrolytic carbon component, typically based on    either oxidation or reduction processes.

Nanotubes can exist as single-walled nanotubes (SWNT) and multi-wallednanotubes (MWNT), i.e. nanotubes having one single wall and nanotubeshaving more than one wall, respectively. In single-walled nanotubes aone atom thick sheet of atoms, for example a one atom thick sheet ofgraphite (also called graphene), is rolled seamlessly to form acylinder. Multi-walled nanotubes consist of a number of such cylindersarranged concentrically. The arrangement in a multi-walled nanotube canbe described by the so-called Russian doll model, wherein a larger dollopens to reveal a smaller doll.

In an embodiment, the nanotubes are multi-walled carbon nanotubes, morepreferably multi-walled carbon nanotubes having on average from 5 to 15walls.

Nanotubes, irrespectively of whether they are single-walled ormulti-walled, may be characterized by their outer diameter or by theirlength or by both.

Single-walled nanotubes are preferably characterized by an outerdiameter of at least 0.5 nm, more preferably of at least 1 nm, and mostpreferably of at least 2 nm. Preferably their outer diameter is at most50 nm, more preferably at most 30 nm and most preferably at most 10 nm.Preferably, the length of single-walled nanotubes is at least 0.1 μm,more preferably at least 1 μm, even more preferably at least 10 μm.Preferably, their length is at most 50 mm, more preferably at most 25mm.

Multi-walled nanotubes are preferably characterized by an outer diameterof at least 1 nm, more preferably of at least 2 nm, 4 nm, 6 nm or 8 nm,and most preferably of at least 10 nm. The preferred outer diameter isat most 100 nm, more preferably at most 80 nm, 60 nm or 40 nm, and mostpreferably at most 20 nm. Most preferably, the outer diameter is in therange from 10 nm to 20 nm. The preferred length of the multi-wallednanotubes is at least 50 nm, more preferably at least 75 nm, and mostpreferably at least 100 nm. Their preferred length is at most 20 mm,more preferably at most 10 mm, 500 μm, 250 μm, 100 μm, 75 μm, 50 μm, 40μm, 30 μm or 20 μm, and most preferably at most 10 μm. The mostpreferred length is in the range from 100 nm to 10 μm. In an embodiment,the multi-walled carbon nanotubes have an average outer diameter in therange from 10 nm to 20 nm or an average length in the range from 100 nmto 10 μm or both.

Preferred carbon nanotubes are carbon nanotubes having a surface area of200-400 m²/g (measured by BET method).

Preferred carbon nanotubes are carbon nanotubes having a mean number of5-15 walls.

Non-limiting examples of commercially available multi-walled carbonnanotubes are Graphistrength™ 100, available from Arkema, Nanocyl™ NC7000 available from Nanocyl, FloTube™ 9000 available from CNanoTechnology, Baytubes® C 150 B available from Bayer Material Science.

In preferred embodiments, said carbon nanotubes are provided as apolyolefin or styrenic copolymer masterbatch. As used herein, the term“masterbatch” refers to concentrates of active material (such as thecarbon nanotubes) in a polymer, which are intended to be subsequentlyincorporated into another polymer (compatible or non-compatible with thepolymer already contained in these masterbatches). Use of carbonnanotubes containing masterbatches makes processes more easily adaptableto industrial scale, compared to direct incorporation of carbonnanotubes powder.

In an embodiment, the composition according to the invention comprisesat least 0.10% by weight of carbon nanotubes, relative to the totalweight of the composition. For example, the composition of the presentinvention can comprise at least 0.30% by weight of carbon nanotubes, forexample at least 0.40% by weight, for example at least 0.45% by weightof carbon nanotubes, relative to the total weight of the composition,preferably at least 0.50% by weight, preferably at least 0.55% byweight, more preferably at least 0.60% by weight, more preferably atleast 0.65% by weight, most preferably at least 0.68% by weight,relative to the total weight of the composition.

In an embodiment, the composition comprises at most 1.75% by weight, forexample at most 1.50% by weight, for example at most 1.25% by weight,for example at most 1.00% by weight, for example at most 0.95%, forexample at most 0.90% by weight of carbon nanotubes, based on the totalweight of the composition.

In an embodiment, the composition comprises:

-   at least 40% by weight of polystyrene or modified-polystyrene, or a    mixture thereof, based on the total weight of the composition,    preferably at least 45%, more preferably at least 50% by weight of    polystyrene or modified-polystyrene, or a mixture thereof;    preferably of high impact polystyrene or a mixture of high impact    polystyrene and polystyrene;-   at least 15% by weight of polyolefin, based on the total weight of    the composition, preferably at least 20% by weight of polyolefin,    preferably at least 25% by weight of polyolefin, preferably at least    30% by weight of polyolefin, preferably at least 40% by weight of    polyolefin, preferably of polyethylene or polypropylene; and-   at most 1.90% by weight of carbon nanotubes, preferably at most    1.75% by weight of carbon nanotubes, preferably at most 1.50% by    weight of carbon nanotubes, preferably at most 1.25% by weight of    carbon nanotubes, preferably at most 1.00%, for example at most    0.95%, for example at most 0.90%, by weight of carbon nanotubes    based on the total weight of the composition.

In an embodiment, the composition comprises:

-   at least 40% by weight of polystyrene or modified-polystyrene, or a    mixture thereof, based on the total weight of the composition,    preferably at least 45% by weight of polystyrene or    modified-polystyrene, or a mixture thereof; preferably of high    impact polystyrene or a mixture of high impact polystyrene and    polystyrene;-   at most 60% by weight of polyolefin, preferably at most 55% by    weight of polyolefin, and at least 15% by weight of polyolefin,    preferably at least 20% by weight of polyolefin, preferably at least    25% by weight of polyolefin, preferably at least 30% by weight of    polyolefin, preferably at least 40% by weight of polyolefin, based    on the total weight of the composition; preferably of polyethylene    or polypropylene; and-   at least 0.10% by weight of carbon nanotubes, preferably at least    0.30% by weight of carbon nanotubes, preferably at least 0.40% by    weight of carbon nanotubes, preferably at least 0.50% by weight,    preferably at least 0.55% by weight, more preferably at least 0.60%    by weight, more preferably at least 0.65% by weight, most preferably    at least 0.68% by weight, and at most 1.90% by weight of carbon    nanotubes, preferably at most 1.75% by weight of carbon nanotubes,    preferably at most 1.50% by weight of carbon nanotubes, preferably    at most 1.25% by weight of carbon nanotubes, preferably at most    1.00% by weight, for example at most 0.95% by weight, for example at    most 0.90% by weight, of carbon nanotubes based on the total weight    of the composition.

The composition may further comprise a styrenic copolymer, preferablywherein the styrenic copolymer is selected fromstyrene-butadiene-styrene block copolymer (SBS) orstyrene-ethylene-butadiene-styrene block copolymer (SEBS).

Preferably, the styrenic copolymer is a styrenic block copolymer.Suitable styrenic block copolymers include at least two monoalkenylarene blocks, preferably two polystyrene blocks, separated by a block ofa saturated conjugated diene, such as a saturated polybutadiene block.Suitable unsaturated block copolymers include, but are not limited to,those represented by the following formulas: A-B—R(—B-A)_(n) orA_(x)-(BA-)_(y)-BA wherein each A is a polymer block comprising a vinylaromatic monomer, such as styrene, and each B is a polymer blockcomprising a conjugated diene, such as isoprene or butadiene, andoptionally a vinyl aromatic monomer, such as styrene; R is the remnantof a multifunctional coupling agent (if R is present, the blockcopolymer can be a star or branched block copolymer); n is an integerfrom 1 to 5; x is zero or 1; and y is a real number from zero to 4.

In an embodiment of the invention, the composition comprises one or moreadditives selected from the group comprising an antioxidant, anantiacid, a UV-absorber, an antistatic agent, a light stabilizing agent,an acid scavenger, a lubricant, a nucleating/clarifying agent, acolorant or a peroxide. An overview of suitable additives may be foundin Plastics Additives Handbook, ed. H. Zweifel, 5^(th) edition, 2001,Hanser Publishers, which is hereby incorporated by reference in itsentirety.

In an embodiment, the composition is free from any compatibilizers.

The invention also encompasses the composition as described hereinwherein the composition comprises from 0% to 10% by weight of at leastone additive such as antioxidant, based on the total weight of thecomposition. In a preferred embodiment, said composition comprises lessthan 5% by weight of additive, based on the total weight of thecomposition, for example from 0.1 to 3% by weight of additive, based onthe total weight of the composition.

In an embodiment, the composition comprises an antioxidant. Suitableantioxidants include, for example, phenolic antioxidants such aspentaerythritoltetrakis[3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate] (hereinreferred to as Irganox 1010), tris(2,4-ditert-butylphenyl) phosphite(herein referred to as Irgafos 168), 3DL-alpha-tocopherol,2,6-di-tert-butyl-4-methylphenol, dibutylhydroxyphenylpropionic acidstearyl ester, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid,2,2′-methylenebis(6-tert-butyl-4-methyl-phenol), hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],benzenepropanamide, N,N′-1,6-hexanediylbis[3,5-bis(1,1-dimethylethyl)-4-hydroxy] (Antioxidant 1098), Diethyl3,5-Di-Tert-Butyl-4-Hydroxybenzyl Phosphonate, Calciumbis[monoethyl(3,5-di-tert-butyl-4-hydroxylbenzyl)phosphonate],Triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate(Antioxidant 245), 6,6′-di-tert-butyl-4,4′-butylidenedi-m-cresol,3,9-bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,(2,4,6-trioxo-1,3,5-triazine-1,3,5(2H,4H,6H)-triyl)triethylenetris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate,Tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, ethylenebis[3,3-bis(3-tert-butyl-4-hydroxyphenyl)butyrate], and2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]octahydro-4,7-methano-1H-indenyl]-4-methyl-phenol.Suitable antioxidants also include, for example, phenolic antioxidantswith dual functionality such 4,4′-Thio-bis(6-tert-butyl-m-methyl phenol)(Antioxidant 300), 2,2′-Sulfanediylbis(6-tert-butyl-4-methylphenol)(Antioxidant 2246-S), 2-Methyl-4,6-bis(octylsulfanylmethyl)phenol,thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol,N-(4-hydroxyphenyl)stearamide, bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate,2,4-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzoate, hexadecyl3,5-di-tert-butyl-4-hydroxy-benzoate,2-(1,1-dimethylethyl)-6-[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenylacrylate, and Cas nr. 128961-68-2 (Sumilizer GS). Suitable antioxidantsalso include, for example, aminic antioxidants such asN-phenyl-2-naphthylamine, poly(1,2-dihydro-2,2,4-trimethyl-quinoline),N-isopropyl-N′-phenyl-p-phenylenediamine, N-Phenyl-1-naphthylamine, CASnr. 68411-46-1 (Antioxidant 5057), and4,4-bis(alpha,alpha-dimethylbenzyl)diphenylamine (Antioxidant KY 405).Preferably, the antioxidant is selected from pentaerythritoltetrakis[3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate] (hereinreferred to as Irganox 1010), tris(2,4-ditert-butylphenyl) phosphite(herein referred to as Irgafos 168), or a mixture thereof.

The composition according to the invention may have improvedconductive-dissipative conductivity. The target resistivity may dependon the particular application (ANSI-ESD F 541-2008). Preferably, thesurface resistivity is at most 10¹¹Ω, preferably at most 10⁸Ω,preferably at most 10⁶Ω, for example at most 10⁵Ω, for example at most10⁴Ω, for example at most 10³Ω. The resistivity can be measured usingthe method described in ASTM-D257, or as described herein after in theexample section.

In an embodiment, the composition comprises at most 1.90% by weight ofcarbon nanotubes, preferably at most 1.75% by weight of carbonnanotubes, preferably at most 1.50% by weight of carbon nanotubes,preferably at most 1.25% by weight of carbon nanotubes, preferably atmost 1.00%, for example at most 0.95%, for example at most 0.90%, byweight of carbon nanotubes based on the total weight of the composition;and a surface resistivity of at most 10¹¹ ohm, preferably at most 10⁸ohm, preferably at most 10⁶ ohm, for example at most 10⁵ ohm, forexample at most 10⁴ ohm, for example at most 10³ ohm.

The present invention also encompasses a process for preparing anconductive composition made of the present composition, said processcomprising the steps of:

-   (a) providing a masterbatch comprising at least 5% by weight of    carbon nanotubes based on the total weight of the masterbatch, and a    polyolefin and/or a styrenic copolymer;-   (b) blending the masterbatch of step (a) with polystyrene or    modified-polystyrene or mixture thereof, and with a polyolefin,-   in amounts such that the conductive composition is obtained which    comprises at most 1.90% by weight of carbon nanotubes, based on the    total weight of the composition.

Suitable polystyrene or modified-polystyrene, styrenic copolymer,polyolefin and nanotubes can be as defined above.

As used herein, the term “masterbatch” refers to concentrates of activematerial (such as the carbon nanotubes (CNT)) in a polymer, which areintended to be subsequently incorporated into another polymer(compatible or non-compatible with the polymer already contained inthese masterbatches). Use of masterbatches makes processes more easilyadaptable to industrial scale, compared to direct incorporation of CNTpowder. In an embodiment, the masterbatch comprises at least 5% byweight of carbon nanotubes based on the total weight of the masterbatch.Preferably the masterbatch comprises at least 8% by weight of carbonnanotubes based on the total weight of the masterbatch. Preferably themasterbatch comprises at least 10% by weight of carbon nanotubes basedon the total weight of the masterbatch. Preferably the content of carbonnanotubes in the masterbatch is comprised between 5 and 30% by weight,preferably between 8 and 20% by weight based on the total weight of themasterbatch.

To form a masterbatch, the CNT and polymer powders may be mixed in amixer which is either integrated into the processing equipment, orpositioned upstream of the latter.

In some embodiments, the step (b) of the present process is performed byadding simultaneously polystyrene or modified-polystyrene or mixturethereof, the polyolefin and the carbon nanotubes masterbatch.

In an embodiment, the polyolefin of step (b) or, if any in step (a), isselected from the group consisting of polyethylene, polypropylene orcombination thereof. Preferably, the polyolefin is polyethylene.

In a preferred embodiment, the polyolefins of step (a) and (b) are thesame.

In an embodiment, in step (a) of the present process, when a masterbatchcomprising styrenic copolymer is used, the content of the styreniccopolymer in the conductive composition is comprised between 1 and 25%by weight, preferably between 2 and 20% based on the total weight ofsaid composition.

This mixing of powders, blends and masterbatch, may be carried out inconventional synthesis reactors, blade mixers, fluidized-bed reactors orin mixing equipment of the Brabender, Z-blade mixer or extruder type.According to one variant of the invention, it is thus possible to use apaddle or blade mixer.

In some embodiments, the process can comprise the steps of:

-   blending a masterbatch comprising a polyolefin or styrenic copolymer    and carbon nanotubes (CNT), with a polyolefin to prepare a first    blend; and-   blending a polystyrene and/or modified-polystyrene with said first    blend.

In some embodiments, the process can comprise the steps of:

-   blending a masterbatch comprising a polyolefin or styrenic copolymer    and carbon nanotubes (CNT), with a polystyrene and/or    modified-polystyrene to prepare a first blend; and-   blending a polyolefin with said first blend.

Preferably, the polyolefin forms an immiscible phase in the polystyreneor modified-polystyrene.

In an embodiment, the polystyrene, modified polystyrene or mixturethereof is the major constituent or at least the main continuous orco-continuous polymeric phase. In an embodiment, the polyolefin is theminor constituent in at most a co-continuous or dispersed polymericphase.

In a preferred embodiment, the composition comprises amodified-polystyrene (PS) such as HIPS and a polyethylene (PE) forexample LLDPE. All polymer-polymer or polymer-CNT blends can be made byclassical twin-screw extrusion process.

For example, the composition can be prepared by first making aconductive PS by blending PE-CNT masterbatch with PS or SEBS-CNTmasterbatch with PS. The conductive composition can then be obtained byblending the conductive PS with PE in which the PE phase forms animmiscible phase into the PS. In another example, the composition can beprepared by first making a conductive PE by blending PE-CNT masterbatchwith PE or SEBS-CNT masterbatch with PE. The conductive composition canthen be obtained by blending the conductive PE with PS. In anotherexample, the conductive composition can be prepared directly by blendingPS, PE and PE-CNT masterbatch or SEBS-CNT masterbatch where conductivePS will be prepared in situ and PE phase forms an immiscible phase intothe PS. The same process can be used to prepare conductive compositioncomprising polystyrene, a polyolefin and CNT, wherein the polyolefin ispolypropylene, low density or high density polyethylene, and the like.

The invention also encompasses formed articles comprising thecomposition according to the first aspect of the invention.

The composition may be suitable for typical injection, extrusion andstretch blow molding applications, but also thermoforming, foaming androtomolding. The articles made according to these processes can be mono-or multilayer, wherein at least one of the layers comprises thecompositions of the invention.

Articles made from the composition may be commonly utilized inmaterial-handling and electronic devices such as packaging film, sheetsand thermoformed objects therefrom, chip carriers, computers, printersand photocopier components where electrostatic dissipation orelectromagnetic shielding are important requirements. Preferably, theformed article comprises packaging. Preferably, the formed articlecomprises electronics packaging.

The invention provides new conductive-dissipative compositions andmaterials therefrom comprising low amounts of CNT, below 1.9% by weight.Preferably, the composition is a blend of at least two immisciblepolymers: polystyrene and polyolefin.

Such compositions are economically viable in comparison to usualconductive-dissipative compounds filled with carbon black. The advantageof the present conductive-dissipative composition comprising carbonnanotubes over those comprising carbon black are less alteration ofmechanical properties, higher processability, smoother part surface,cleanliness, lower part warpage, less outgasing of volatiles andmaterial downgauging.

The present invention also encompasses a composition comprising at leasttwo immiscible phases: a polystyrene phase comprising polystyrene ormodified-polystyrene, or a mixture thereof, and a polyolefin phasecomprising a polyolefin, wherein said composition further comprisescarbon nanotubes, in a concentration of at most 1.90% by weight, basedon the total weight of the composition.

The present invention can be further illustrated by the followingexamples, although it will be understood that these examples areincluded merely for purposes of illustration and are not intended tolimit the scope of the invention unless otherwise specificallyindicated.

EXAMPLES

Blends according to embodiments of the invention were prepared using atwo step process. The blends comprised polystyrene, linear low densitypolyethylene and carbon nanotubes.

For the carbon nanotubes (CNT), multi-walled carbon nanotubes Nanocyl™NC 7000, commercially available from Nanocyl, were used. These nanotubeshave a surface area of 250-300 m²/g (measured by BET method), a carbonpurity of about 90% by weight (measured by thermal gravimetricanalysis), an average diameter of 9.5 nm and an average length of 1.5 μm(as measured by transmission electron microscopy).

For the polystyrene polymer, high impact polystyrene (HIPS) PolystyreneImpact 8350, available from Total Petrochemicals, was used. PolystyreneImpact 8350 has a melt flow index of 4.5 g/10 mn as measured accordingto ISO 1133 H (200° C.-5 kg) a Rockwell hardness of R 54 (ISO 2039-2), aDensity of 1.04 g/cm³ (ISO 1183), a Surface resistivity>10¹³ Ohms asmeasured according to ISO IEC 93.

For the polyethylene polymer, linear low density polyethylene (LLDPE)Total 1810, available from Total Petrochemicals was used. LL 1810 is anethylene-butene copolymer produced in a gas phase reactor. LL1810 has adensity of 0.919 g/cm³ as measured according to ISO 1183, and a MeltFlow Rate 1.0 g/10 min as measured according to ISO 1133 (190° C./2.16kg).

Commercially available polyethylene/carbon nanotubes masterbatch(MB-PE-CNT), PLASTICYL™ LDPE2001, and SEBS/carbon nanotubes(MB-SEBS-CNT), PLASTICYL™ SEBS1001 were used to exemplify the presentprocess. A conductive-dissipative high impact polystyrene(HIPS)-LLDPE-blend was prepared by blending using classical twin-screwextrusion process, high impact polystyrene (HIPS) Total 8350 with linearlow density polyethylene (LLDPE) and carbon nanotubes masterbatch,either MB-PE-CNT or MB-SEBS-CNT in Brabender co-rotating twin screwextruder using the same extrusion parameters as in step 1. Comparativeexamples consisted of high impact polystyrene (HIPS) Total 8350 blendedwith high impact polystyrene carbon nanotubes masterbatch (MB-PS-CNT).

The content of the blends in % by weight are shown in Table 1(HIPS-PE-CNT compounds, examples 1-2) and Table 2 (HIPS-CNT compounds,comparatives examples 9-12). Comparative examples (9-12) consisted ofhigh impact polystyrene (HIPS) Total 8350 blended with high impactpolystyrene carbon nanotubes masterbatch (MB-PS-CNT).

The content of carbon nanotubes in % by weight in blends (% CNT) wasdetermined by thermal gravimetric analysis (TGA) according to ISO 11358and ASTM E1131, using a Mettler Toledo STAR TGA/DSC 1 apparatus. Priorto the determination of the content of carbon nanotubes in % by weightin blends (% CNT), the carbon content of the carbon nanotubes in % byweight (% C-CNT) was determined: 2 to 3 milligrams of carbon nanotubeswere placed into a TGA. The material was heated at a rate of 20° C./minfrom 30° C. to 600° C. in nitrogen (100 ml/min). At 600° C., the gas wasswitched to air (100 ml/min), and the carbon oxidized, yielding thecarbon content of the carbon nanotubes in % by weight (% C-CNT). The %C-CNT value was the average of 3 measurements. For the content of carbonnanotubes % by weight in blends (% CNT), 10 to 20 milligrams of samplewas placed into a TGA. The material was heated at a rate of 20° C./minfrom 30° C. to 600° C. in nitrogen (100 ml/min). At 600° C., the gas wasswitched to air (100 ml/min), and the carbon oxidized, yielding to thecarbon content of carbon nanotubes in the sample (% C-sample). The %C-sample value was the average of 3 measurements. The content of carbonnanotubes % by weight in sample (% CNT) was then determined by dividingthe carbon content of carbon nanotubes % by weight in samples (%C-sample) by the carbon content of the carbon nanotubes in % by weight(% C-CNT) and multiplying by 100.% CNT=% C-sample/% C-CNT*100

The surface resistivity (SR) of the blend was measured using a 2410SourceMeter® apparatus. Conditions which were used were similar to thosedescribed in the CEI 60167 and NF C26-215 test methods. The surfaceresistivity (SR) was measured on 2 mm thick compression molded plaque at200° C. during 12 minutes. The resistance measurement was performedusing an electrode system made of two conductive paint lines usingsilver ink and an adhesive mask presenting 2 parallel slits 25 mm long,1 mm wide and 2 mm apart. The samples were conditioned at 23° C./50% RHfor minimum 4 hours before running the test. The measure of theresistance in ohm was reported to a square measurement area andexpressed in ohm/square using the following equation: SR=(R×L)/d,wherein: SR is the average resistance reported to a square measurementarea, conventionally called surface resistivity (expressed in ohm/sq), Ris the average of the resistance measurements (ohm), L is the paint linelength (cm), d is the distance between the electrodes (cm). L=2.5 cm andd=0.2 cm and SR=R×12.5. The surface resistivity (SR) value was theaverage of 3 measurements.

The results of the measurement are shown in Table 1 and Table 2.

TABLE 1 examples Blends 1 2 % HIPS 49.5 59.4 % PE 49.5 39.6 % CNT 0.970.98 SR (ohm/sq) 9 10³ 1 10⁴

TABLE 2 comparative examples Blends 9 10 11 12 % HIPS 98.59 98.45 98.1897.94 % CNT 1.41 1.55 1.82 2.06 SR (ohm/sq) 1 10⁶ 4 10⁴ 3 10⁴ 8 10³

The blends prepared by the process according to the invention, inparticular when carbon nanotubes were provided in a polyolefinmasterbatch, had a good surface resistivity even at low concentration inCNT as demonstrated above.

Excellent results were also obtained for compositions prepared accordingto the present process wherein carbon nanotubes were provided in a SEBSmasterbatch. Good surface resistivity was also measured in these lattercompositions comprising SEBS even at low concentration in CNT in thesample (1 wt % CNT).

The invention claimed is:
 1. A process for preparing a conductivecomposition comprising: (a) providing a masterbatch comprising at least5% by weight of carbon nanotubes based on a total weight of themasterbatch, and a polyolefin and/or styrenic copolymer; (b) blendingthe masterbatch of step (a) with a blend of polystyrene, or high-impactpolystyrene, or a mixture thereof, and a polyolefin, in amounts suchthat the conductive composition is obtained, wherein the conductivecomposition comprises at most 1.90% by weight of carbon nanotubes, basedon the total weight of the conductive composition; wherein theconductive composition has a surface resistivity of at most 10⁴ Ohm/sq,measured in accordance with ASTM-D257.
 2. The process according to claim1, wherein the conductive composition comprises at least 30% by weightof the polystyrene, the high-impact polystyrene, or the mixture thereof,based on the total weight of the conductive composition.
 3. The processaccording to claim 1, wherein the conductive composition comprises atleast 50%, by weight of the polystyrene, the high-impact polystyrene, orthe mixture thereof, based on the total weight of the conductivecomposition.
 4. The process according to claim 1, wherein the conductivecomposition has a surface resistivity of at most 10³ Ohm/sq, measured inaccordance with ASTM-D257.
 5. The process according to claim 1, whereinthe conductive composition comprises at least 0.3% and at most 1.90% byweight of carbon nanotubes relative to the total weight of theconductive composition.
 6. The process according to claim 1, wherein theconductive composition comprises at least 0.5% and at most 1.90% byweight of carbon nanotubes relative to the total weight of theconductive composition.
 7. The process according to claim 1, wherein thepolyolefin of step (b) and, if any in step (a), is polyethylene,polypropylene, or a combination thereof.
 8. The process according toclaim 7, wherein the polyolefin of step (b) and, if any in step (a), ispolyethylene.
 9. The process according to claim 7, wherein thepolyolefins are used in both steps (a) and (b), and wherein thepolyolefins of step (a) and step (b) are the same.
 10. The processaccording to claim 1, wherein the conductive composition comprises atleast 15% by weight of the polyolefin, based on the total weight of theconductive composition.
 11. The process according to claim 1, whereinthe masterbatch comprises the styrenic copolymer, or the styreniccopolymer and the polyolefin; and wherein the styrenic copolymer isstyrene-butadiene-styrene block copolymer (SBS) orstyrene-ethylene-butadiene-styrene block copolymer (SEB S).
 12. Theprocess according to claim 11, wherein the content of the styreniccopolymer in the conductive composition ranges between 1 and 25% byweight, based on the total weight of the conductive composition.
 13. Theprocess according to claim 11, wherein the content of the styreniccopolymer in the conductive composition ranges between 2 and 20% byweight, based on the total weight of the conductive composition.
 14. Theprocess according to claim 1, wherein the content of carbon nanotubes inthe masterbatch ranges between 5 and 30% by weight, based on the totalweight of the masterbatch.
 15. The process according to claim 1, whereinthe content of carbon nanotubes in the masterbatch ranges between 8 and20% by weight, based on the total weight of the masterbatch.
 16. Anarticle made of the conductive composition prepared by the process ofclaim
 1. 17. The process according to claim 1, wherein the conductivecomposition comprises at least 15% and at most 60% by weight of thepolyolefin; at least 30% by weight of the polystyrene, the high-impactpolystyrene, or the mixture thereof; and at least 0.1% and at most 1.90%of the carbon nanotubes; each based on the total weight of theconductive composition.
 18. The process according to claim 1, wherein,in step (b), the polyolefin comprises linear low density polyethylene.19. The process according to claim 1, wherein the conductive compositioncomprises at least two immiscible phases comprising a polystyrene phaseand a polyolefin phase.
 20. The process according to claim 1, whereinthe composition comprises at least 30% by weight high-impactpolystyrene, or at least 30% by weight a mixture of polystyrene and highimpact polystyrene.
 21. The process according to claim 20, wherein thecomposition comprises at least 50% by weight high-impact polystyrene, orat least 50% by weight a mixture of polystyrene and high impactpolystyrene.